446 CANADIAN" EQUIVALENTS. TCh. XXVIL 



erroneously identified, an error to which he confesses that he himself con- 

 tributed ; and on the whole these lower beds contain, he thinks, a very 

 distinct set of species, only three or four of them out of eighty-three 

 passing upwards into the incumbent formations.* 



Be this as it may, the Black River Limestone, No. 15, contains certain 

 forms of Orthoceras of enormous size (some of them 8 or 9 feet long !), 

 of the subgenera Ormoceras and Endoceras, seeming to represent the 

 Lower Silurian or Orthoceras limestone of Sweden. Moreover, the gen- 

 eral facies of the fauna of all these beds is essentially similar. Another 

 ground for extending our comparison of the Llandeilo beds of Europe as 

 far down as the calciferous sandstone is derived from the researches of 

 Mr. Logan in Canada, and the study by Mr. Salter of the fossils collected 

 by the Canadian Surveyor near the S. E. end of the Ottawa River, where 

 one mass of limestone incloses species common to all the beds from the 

 Calciferous Sandstone (No. 18) up to the Trenton Limestone (No. 14). 

 In this rock, the Asaphus gigas and other well-known Trenton species are 

 blended with the Maclurea (a left-handed Euomphalus, fig. 606), a genus 



Fossils from Allumette Rapids, River Ottawa, Canada. 

 a Fig. 606. 



Maclurea Logani, Salter. 

 a. View of the shell. b. Its curious operculum. 



characteristic of the Chazy Limestone, or No. 1 7 ; F1 =- 60T - 



and Murchisonia gracilis (fig. 60*7) is another 

 Trenton Limestone species found in the same Silu- 

 rian limestone of Canada ;f while one of the most 

 common shells in it is the Raphistoma ? {Euom- 

 phalus) uniangulatum, Hall, a species character- 

 istic in New York of the Calciferous Sandstone 



itself. Murchuonia gracilis, HaU. 



r n j • xi cii i e -vr it i ii A fossil characteristic of the 



In Canada, as in the State 01 jNew lork, the Trenton Limestone. The 



Potsdam Sandstone underlies the above-mentioned ggjg c r ° ^ on in Loww 

 calcareous rocks, but contains a different suite of 

 fossils, as will be hereafter explained. In parts of the globe still more 

 remote from Europe the Silurian strata have also been recognized, as in 

 South America, Australia, and recently by Captain Strachey in India. 

 In all these regions the facies of the fauna, or the types of organic life, 

 enable us to recognize the contemporaneous origin of the rocks ; but the 

 fossil species are distinct, showing that the old notion of a universal dif- 

 fusion throughout the " primaeval seas" of one uniform specific fauna was 



* Hall ; Forster and "Whitney's Report on Lake Superior, Pt, II. 1851. 

 f Logan, Report Brit Assoc. Ipswich, pp. 59, 63. 



